Fluid reactive surface



Oct. 11, 1932. c. H. A. F. R055 1,832,164

FLUID REACTIVE SURFACE Filed Ila." 8. 1931 3 Sheets-Sheet 1 0562s: 0/ lilac gwumtoc (manHAH/Ross Oct. 11, 1932. 055 fl,882,164

FLUID REACTIVE SURFACE Filed May a, 1931 v 3 Sheets-Sheet 2 Bus e Ling Patented Oct. H, 1932,

stares Y CHARLES H. A. F. L. ROSS, OF WASHINGTON, DISTRICT OF COLUMBIA.

FLUE REACTIVE SURFACE Application filed May 8, 1931. Serial No. 536,006.

of the characteristics of such object-f It is of particular utility with respect to such objects having a helical surface.

The invention further involves the means used to carry out this method.

One particular application of the invention is its use in marine propellers of the screw type, although the invention-is broadly susceptible of use in turbines, fans, aeroplane V propellers, fluid drivendevices such as wind mills, and, in general, any device having a surface or surface driving,'or being driven a fluid. v

In shipbuilding practice, the screw propeller dominates the field ofpropulsion devices for self-propelled ships, and its use is practicallyuniversal on ocean-going steames. The use of the more cumbersomepad le wheels has beenv restricted to the relatively small ships on inland waters. Yet, while the screw propeller has a. number of constructional advantages,- it has been, as previously made, a ,relatively-inelficient device, and

' wastes at least forty per cent of'the power-Q delivered to it by the driving engines.

Inspite of the decided improvementslin re cent years in otherparts of the driving mech .40 anism, such as the use of steam turbines, the

use of oil as fuel,etc., the screw ropeller has remained a wasteful device. uch improvements as were made therein were largely the result of empirical or out and try methods, and in some cases, the result of accidental discoveries. A typical example is the reduction in the number of the blades, which resulted from the observation that a steamer driven by a six-bladed propeller ac- .tually went faster after one of the blades was accidentally lost. Other developments were changes in area of the blades,contour or shape of the blades, etc., made with the hope of producing a more efficient propeller.

About the time when increased speeds were beginning to be used in steamers, it was noticed that there was a rapid'loss'of elficiency in the screw propellers at the higher speeds of rotation. This led to the pronouncement of the cavitation theory by Mr. Sidney W. Barnaby. This theory attributes the increased loss of efliciency to the cavity produced about the propeller after it reaches a certain speed, because of the inability of the fluid to flow fast enough to follow the blade. To avoid this effect, the use of a propeller with larger area was recommended.

Despite all these developments, however, the screw propeller has remained a relatively inefiicient device. to the ignoring of a fundamental factor in the manufacture ofpropellens. To fully understand this factor, a consideration of what I term the wart? theory is necessary. It may be stated at the outset, however,'that this 75 theory is based upon an extensive study and observation of the action of propellers, and that the change-of construction based thereon has resulted an increasedefliciency of some twenty-five to thirty per cent. so

' In presentprac'tice, thefinished, propeller" is notfrequired to be accurate within certain limits-,andapparently the only requirement this respectisthat the surfaces of the blades look satis ctorily -sinooth to the eye.

The industry see s to have accepted the conclusion that the screw propeller is inherently inefiicient and that refinements in the accuracy of the surface are a mere waste of time.

In present propellers, therefore, even of the This is due, it is believed, 7o.

best grade, there exists inequalities in the surfaces, such as lumps or warts. These form high spots and corresponding valleys in the surface, and have been found to have a decided effect upon the etficiency of the propeller. It is believed that when. the propeller is driven at its usual speed, the water hits only these high spots, and skips past the valleys. The water does not follow the blade, and a decided loss in eflieiency consequently results. The action may be compared to a solid tired automobile passing over a rough road at high speed, causing the driving wheels to be repeatedly in the air. During such times, the power delivered to the wheels is entirely lost, so far as propelling the vehicle is concerned, and the efliciency of the automobile is greatly reduced.

In view of this it is apparent that the accu-' rate machining of the blades to form a smooth surface free from such warts produces an increased efficiency of the propeller. In actual practice, this increase is found to be not a mere minorincrease such as might be expected from more accurate methods, but the unexpected result of an increase ofsome twenty-five to thirty per cent in efliciency.

The abolition of the turbulence arising .from warts promotes the maintenance of the original even surface. In addition, the smooth passage of the water over such a surface so greatly reduces vibration that it becomes inappreciable. and this further increases the relative efliciency of the propeller.

It is accordingly 9. major purpose of my invention to provi e a method for accurately laying out a propeller, or other similar object.

It is another object of my invention to provide an accurate method for determining and illustrating the developed arcuate sections of a propeller or other similar object.

It is a further object of my invention to provide a method of accurately determining the desired theoretical surface of a propeller blade or other similar object, in order that such surface may be reproduced on an actual propeller blade, and such actual blade checked y comparison thereto.

It is a further purpose of my invention to carry out the above objects with particular reference to a truly helical propeller blade.

With further reference to a truly helical propeller blade, it is a still further object of my invention to provide means for determining the helix angle and other correlated functions of any arcuate section of-such a blade. As indicated above, my invention is suscep-' tible of use in aeroplane propellers. or other propellers. act ng on a gaseous medium; in

turbines, 'driven'either by a liquid or a gas;

' in fans or blowers driving a gaseous medium;

:wind mills or, in fact, any device havin a in devices driven by afluid medium such as moving sur ace cooperating'with a fluid. ccordingly, while I showparticul'arly in this specification a marine screw propeller as the means for carrying my invention into practi cal effect, I do not limit myself to this particular construction, which for purposes of explanation, has been made the subject of illustration.

It is accordingly :1. further and broader object of my invention to increase the efficiency of surfaces used in coact-ion with a fluid medium.

\Vith these and other objects in View, which may be incident to my improvements, the invention consists in the parts, combinations, and methods hereinafter set forth, with the understanding that variations therein may be carried out. without departing from the spirit of the invention or the scope of the appended claims.

In the drawings:

Figure 1 is the representation of a propeller tested inthe investigation.

Figure 2 is the graph of the variation in lead at various portions of the surface of a propeller of good grade.

Figure 3 is a diagrammatic sketch showing how the various points plotted were measured.

Figure 4 is a corresponding graph of the surfaces of a propeller produced in accordance with my invention.

Figure 5 illustrates a plan of a propeller with the measurements to be taken therefrom indicated thereon. a

Figure 6 illustrates the sections of a propeller developed according to my method.

Figure 7 illustrates a section of a propeller with a circularly curved back.

Figure 8 is a construction used toillustrate the Koff law.

Figure 9 is a construction used to explain my method of showing developed surfaces of a propeller.

Figure 1 shows the results of a test made on a good grade of propeller of the type now produced. The blades of this propeller were painted with black paint, and the propeller was then usetbin actual service. This figure shows how the paint was worn, thewhite portions on the blades being the metal surfaces from which the friction of the water removed the paint. As is indicated, the paint is not worn off smoothly, but is worn off at numerous high spots on the blade. About the middle of one of the blades, indicated by the arrow, there is a radially extending valley practically unbumpiness, causing a vicious circle which, it is believed, causes the relatively low efficiency of the screw propeller as now made.

With a propeller made in accordance with the present invention, aside from the marked increase in efiiciency, there is a decided reduction in vibration, which in itself causes a more efficient action of the propelling mechanism, as well as materially increasing the life and dependability thereof.

There is another result from the lack of mechanical accuracy in finishing the blades, and this is the wide variation in the lead as determined from various points of the blade. Theoretically, the surfaces of the typical screw propeller is helical, with a certain definite lead. With'even the best type of present propeller, however, the lead, as calculated from various points of the surface,

varies greatly. Figure 2 is a graph indicating'such variation, and Figure 3 shows how the various points were determined. To draw the graph for the points on the three inch radius, the points are determined as being a certain number of degrees from the base line, which degrees are plotted "as abscissze, and the various leads found for these points respectively, are plotted as ordinates. The graph shows that there is no definitely fixed lead, or any definite variable lead bearing a continuous relation to a helical surface.

The lead on the propeller graphed is mere ly a hit or miss value varying from about twenty-two and onehalf inches to twenty four and'one half inches. Such variations mean that the water is impelled at different rates at difl'erent parts of the surface, and

such action unquestionably causes eddies and other undesirable eifects 'and decidedly reduces the efiiciency of the propeller.

Figure 4 shows a corresponding diagram of a propeller made according to my invention, and the uniform lead thereof, resulting in a uniform and steady imp-ulsion, is apparent from the diagram.

Thus,it is appareht that the basic feature of my invention is the provision of a regular, even, smooth surface for the blades of a pro peller, and a surface which follows, as accurately as possible, the theoretical surface desired. Such a surface I term a wartless surface, and a propeller having such surfaces, a wartless propeller.- Both the pushing and pulling surfaces of, the blades should be such wartless surfaces.

, To provide such a surface, I use a profile grinder of the type disclosed in my application Serial No. 501,155, filed December 8.-

1930 and my application Serial No. 517,566, filed February 21, 1931. It is to be understood that those disclosures are hereby made apart of the disclosure of this present appli-' cation. By such machines, the production of a smooth, uniform, wartless surface may of suitable templates, any desired type of sur- I face may be produced on the blades, and such surface will approach the desired theoretical surface to within L003 inch.

With regard to the above disclosure, this application is a continuation in part of my application Serial No. 531,784, filed April 21,1931. v

Figure 5 illustrates the arcuate sections which are accurately developed by my method, the arcs described on the propeller blade indicating the cylindrical planes upon which sections are taken. Figure 6 is a typical showing of such developed surfaces.

The basis for the development and location of points .on a propeller or other similar surface goes to the fundamental proposition of locating such points and developing a section of the propeller from two reference points. These reference points are as fol- I lows 1. The axis of revolution.

2. A point to or from which all angular measurements are related.

In considering these points, a one plane system of coordinates is used, one quadrant only being employed. The Y-axis is the axis of rotation of the propeller and the X-axis forms what is termed a base line rotatable about the Y-axis upon which is laid off from the origin the radii of points desired to be located. I v

The base line just referred to is swung about the origin until it is tangent with some point'on the trailing edge of the blade, as shown in Figure 5. This point is chosen arbitrarily, :and is a point equal to ths of the radius of the propeller. All arcuate'de grees are measured from the base line in the position last mentioned, thertotal arcuate angle, as shown in Figure 5, being 108?, this and that on the right, (see Figure 5) is full. It appears that 'the location of the line on the right, or the full base line, could be" positions at any numberof degrees from the leading edge so longas it would not cross any portion of the propeller blade.

Turning now to Figure 6, it will be noted that the base line, which is shown as the X.- axis, has plotted thereon various radii, while the Y-axis, the axis of revolution, has plotted thereon the angular degrees from the locating point or the trailing edge of the propeller.

Before giving further discussion in connection with Figure 7, it is thought to be wise to consider what I term the Koif law. I define Kofi as equal to Now if Kotf is laid off on the Y-axis, see Figure 8, and a line is drawn through its upper extremity parallel to the X-axis, and a perpendicular'is erected upon the base line, or the X-axis, three times as far from the origin as the radius being developed, if a line is drawn through the intersection of the perpendicular to the base line and the parallel to the base line, and through the point on the base line representing the radius chosen,

this line will form an angle with the base line equal to the helix angle ofthe propeller for the particular radius.

This may be proved in the following manner:

lead L circumference 2?]? Hence BA C"=helix )Z.

. But tan of helix a gas will be explained below), while on .the

-axis the radii in inches are plotted.

A calculation for a point at from the trailing edge for a 4" radius will be given for a propeller whose lead equals- 23" and whose diameter is 20".

The following constants should be derived:

Koif==%= =7.321 inches To change degrees into inches of elevation of the particular point under discussion (i. e. a point 50 from the trailing edge) from the plane of the base line use the following formula:

degrees included by blade Inches= 6 L Hence a constant, and in the example p L 23 a Hence ase line on the drawings' and 50 would=.0638X 50=3.19 inches perpendicular distance between the 50 points and the plane of the base line.

Now with particular reference to Figure 6, suppose information .upon a point at 4" radius and 50 from trailing edge is desired. This would be obtained by the use of the coordinates shown. For full graphic showing see Figure 9. At 4" radius line B'A would be-drawn according t othe Koff law so as to make an angle with X-axis equal to the helix angle.

By construction B'A0=helix angle. Also line B'A represents the developed helix for a four inch radius on the pushing face of the propeller.

Information on a point B at 50 is desired. The 50 distance is plotted on axis of rotation, and a line parallel to base line drawn. The intersection of this parallel with the line B'A locates point B on the pushing face of the propeller.

Of course, by design, the lead of the propeller is known. Hence, line'BA can be drawn. Also by design, and this is important to note, the designer chooses the shape of the pulling surface of the ropeller. This is represented by the line which crosses 50 line at W and whose angle with BA is known by design.

Now draw AY perpendicular to base line and drop the perpendicular BC to base line.

Fora 4" radius and 23" lead and-d: BAO= 42 28 and a IBAY=Y47 32'.

Nowdraw line BD from B perpendicular to AB and at D erect DE perpendicular to 50 line. By construction ):DBE= {BAY or the complement of the helix an le. (Two angles whose sides are perpendicu ar each to eachare equal.)

Point B, the one desired, has been located on the pushing face of the propeller. The line BD represents the curve of thickness and line ED the curve of surface.

Obviously other sections along the 4 re;-

dius at different degrees maybe determined,

as. for example, a section at 25 and one at 62 30. Hence a designer will know at a I glance what any section along any radius will look like.

The calculations may be summarized as follows:

Hence 1.0638 and since inches degrees included by blade XL, the 501in e and a sin e: BAO=0.67516 Also ):BAY=90 -42 2s'=47 32' and sin e: BAY= 0.73767 p Now in A BAG the BAG is known and" BC is known.

Hence B0 AB sin {BAG =4.73 inches cotan {BAO= AO= cotan {BAOX B0= 1.09 X 3.19

3.48 inches. In the AJBAD by design the a BAD is known.

Assume {BAD=6 17 Also A-B has been calculated. Hence 0.10949 X 4.73l= 0.518 inches tan {BAD= BD=tan 6 17 oped or expanded length of the helix (4 radius) g L L- I mwm Inches $9 and expanded leiu'gtlgifl I 360 0.0946 inch. I

In summation, the following tableshows F he lengths calculated and the known quansegment of a circle. Such a design tities needed for calculation of the point selected (i. e., a point at on a 4", radius) Lead 23 inches {BAD 6 17 25 gadius t 4 inches Tan {BAD 0.10949 egrees o n t point t 50 B0 3.19 inches 1s ance po 11 from origin 3.19 inches AB 4.73 inches of; 7.321 inches A0 3.48 inches figgg n -2s BD 0.518 inch (82in (FAG t r 0.675 ED d d 0.382 inch omp emen o xpan' e helix (BAY 47 32 length 34.1 inches S1114: BAY 0.737 g 0.0946 inches The pushing face of such sections in Figure 6 I is determined by the Kofi law as explained above. The pulling face is arbitrarily chosen by'the designer.

In the foregoing, it has been stated that the line AD represents the developed pulling surface of the blade. Many designers however, like a, pulling surface which results in a developed section having the appearance ofa is shown in Figure 7 and is also given below.

Again choosing a point B at 50 on a 4: radius it maybe located on the pushing face of the propeller in a manner like that described. To locate points on the ulling face, however, a construction such as l 7 must be made.

With reference to the summation given above, AB=4.731 inches; BD=.518 inch; e: DAB=6 17125", and

sin 6 17 25= 0.10957.

In A DAB AD =2? +BD2, AD /4. 731 0.518 AD +-./22. 4+. 269 =4. 76 in.

Continue BD to left of B. Bisect AD at e,

' Ae=D= inches,

and in the As Due and Ame, the side we is common, the sides Am and De) are equal radii and Ac=cD. Hence the As are equal and. therefore {Dwe= ewA.

Now {Dme= {DAB (Qiswhose sides are perpendicular are equal) and igure S MIDAB 0.i0957T"o.10957 1.75in.

With Do as a radius, the pulling surface of the propeller may be drawn.

To determine any point on this pulling surface, draw from o) the line making any 5 desired (Y with we say an )I of 2. represents any point on the arc AD and, it is'desired to locate this point as well as other points on the arc.

Since a: 4m by assumption=2, the

= V480 22.4 /4575 21.2 inches- Y The DA4 is measured by k the arc 1 (An inscribed angle is measured by its 1ntercepted arc.) But the arc D is also sub- 35 tended by {Dent which is equal to 4 17 O I I, 25 =2 s 43" and 0=2.255 inches.

The coordinates of the point have been located. Obviously other points on the arc- AD may be similarly located by varying the angle (1)13! so that the curve of the back surface of the propeller will be completely described.

From the above constructions, it is apparent that I have provided a method whereby an number points upon the surface of a prope ler may be fully located and whereby the ar- 1 cuate sections of a propeller may be accurate- 1 shown. By such means the machine tools fiir producing a propeller may be accurately set and operated. With machines such as are disclosed in my applications Serial Nos. 0

501,155 and 517,566, above referred to, the form and proper placing of the templates may be accurately determined.

Similarly, the accuracy of an actual propeller-ma'y be checked by comparison to its theoretical surface as determined by my method. It is possible, for instance, to establish certain tolerances in such work, which insures the obtaining of a propeller accurate to within the minimum limits obtainable by careful machining, and the obtaining of a wartless surface, such as I have described previously in this s ecification. Such sur face may thereafter e checked by the above means to determine whether it is within the tolerance set, and whether it is accordingly a true wartless surface.

While I have shown and described the preferred embodiment of my invention, I wish it to be understood that I do not confine myself to the precise details set forth,-by way of illustration, as it is a parent that changes, variations therein an other applications thereof may be made by those skilled in the art, without departing from the s irit of the invention or exceeding the scope of the claims.

I claim: I

1. The method of determining the shape of an arcuate section of any desired radius of a propeller blade which comprises constructing a developed section thereof correlated to a vertical axis indicating degrees'of arc and distance" parallel to the axis of rotation, and to a horlzontal axis indicating. length of radius and distance measured arcuately.

7 about the axis of rotation, determining the pushing face of said section by connecting a point distant three radii from the vertical axis and distant an amount equal to the leadof the propeller divided or from the horizontal axis with a point the horizontal axisdistant one radius from the vertical axis,

locating the points of such section at the leading and tralhng edges of the propeller in said ushin face, and constructing the pulling ac'e of t e propeller in any desired manne 2. The method of determining of a number ofarcuate sections 0 blade in the manner specified in claim 1.

the shape a propeller 3. The method of producing a propeller blade which comprises successively machining circumferential portions of it to simulate corresponding sections determined as in claim 1. i I

4. The method ofchecking the accuracy of a propeller which comprises comparing the actual propeller to sections determined as in claim 1.

5. The method of determining the shape of an arcuatesection .of any desired radius of a propeller blade as in claim 1, and in addition, the steps of determining the pulling face of said section having a given thickness at its middle point, comprising determining the radius of a circle that would pass through the leading and trailing points of said section and the mid-point of said pulling face and drawing an arc of said radius through said leading and trailing points and said mid-point, to constitute the pulling face of said section.

6. The method of producing a wartless propeller which comprises determining the shape of a number of arcuate sections thereof correlated to avertical axis indicating degrees of arc and distance parallel to the axis of rotation, and to a horizontal axis indicating length of radius and distance measured arcuately about the axis of rotation, by determining the pushing face of said sections by connecting, for each face, a, point distant three radii from the vertical axis and dis-.

tant an amount equal to the lead of the propeller divided by 1r from the horizontal axis with a point in the horizontal axis'distant' one radius from the vertical axis, locating the points of such section at the leading and trailing edges of the propeller in said pushing face, and constructing the pulling face of the propeller in any desired manner; machining the propeller to reproduce in it the sections so calculated, and checking the propeller by comparing actual measurements thereof to the desired values obtained in the developed sections, the tolerancefor the actual lead obtained "in such checking to be within four per cent of the theoretical lead.

In testimony whereof I afiix my signature.

CHARLES H. A. F. L. ROSS. 

